The Modular Multilevel Converter (MMC) realizes high-voltage and large-capacity output by sequentially cascading several converter valve sub-module units in the same direction, without the need for direct series connection of switching devices, which avoids the requirement of uniform triggering for direct series connection of devices, and has many advantages such as low switching frequency, good expansibility, high quality of output voltage waveform and low operation loss, it is therefore widely used in flexible AC and DC transmission applications, and currently it has been widely used in power supply, back-to-back interconnection and large-scale renewable energy grid connection in island and urban load-intensive areas, and has broad prospects for development.
The MMC medium-voltage distribution network needs to realize DC fault isolation and fast recovery after a fault occurs, and the use of the converter valve topology with self-shutdown capability is an optimization scheme, but the converter valve topology scheme with self-shutdown capability leads to high loss of converter, so a hybrid topology scheme using half-bridge and full-bridge is a preferred solution. However, for this scheme, if half-bridge MMC sub-module is used partly and full-bridge MMC sub-module is used partly in a direct way, the commonality of sub-modules is not good and the sub-modules cannot be interchanged, it is therefore feasible to design a reconfigurable MMC sub-module unit without additional cost.
Meanwhile, the MMC dynamic model experiment system simulates the working state of modular multilevel converter to verify key technologies such as the actual engineering control protection strategy and the control strategy for the valve-based electronic control system, which is an important technical means to study modular multi-level converter at present.
The MMC sub-module unit topology commonly used in engineering comprises a half-bridge structure, a full-bridge structure, a quasi-full-bridge structure, etc. However, the currently constructed MMC dynamic simulation experiment platform generally has the disadvantages of single topology of dynamic simulation sub-module unit and not easy to adjust flexibly, which cannot realize the transformations of multiple topologies in one sub-module unit. When the topology of simulation sub-module unit changes, the requirements of dynamic simulation experiment cannot be met, and a new dynamic simulation experiment platform needs to be rebuilt. If a dynamic simulation experiment platform is built separately for different MMC sub-module topologies, the workload will be large and the construction cost will be high, and the MMC dynamic simulation experiment platform will be inefficient. Therefore, MMC dynamic simulation sub-module units with multiple typical topological switching capabilities are of great significance.